1. Field of the Invention
The present invention relates to fitting of cochlear implants, and in particular to an electrode array fitting which allows the auditory nerve to be stimulated by both acoustic and electrical stimuli.
2. Related Art
Cochlear implants have been developed to assist people who are profoundly deaf or severely hearing impaired, by enabling them to experience a hearing sensation representative of the natural hearing sensation. For most such individuals the hair cells in the cochlea, which normally function to transduce acoustic signals into nerve impulses which are interpreted by the brain as sound, are absent or have been partially or completely destroyed. The cochlear implant therefore bypasses the hair cells to directly deliver electrical stimulation to the auditory nerve with this electrical stimulation being representative of the sound.
Cochlear implants have traditionally consisted of two parts, an external speech processor unit and an implanted receiver/stimulator unit. The external speech processor unit has been worn on the body of the user and its main purpose has been to detect the external sound using a microphone and convert the detected sound into a coded signal through an appropriate speech processing strategy.
This coded signal is then sent to the receiver/stimulator unit which is implanted in the mastoid bone of the user, via a transcutaneous link. The receiver/stimulator unit processes the coded signal into a series of stimulation sequences which are then applied directly to the auditory nerve via a series or an array of electrodes positioned within the cochlea, proximal to the modiolus of the cochlea. One such cochlear implant is set out in U.S. Pat. No. 4,532,930, the contents of which are incorporated herein by reference.
With improvements in technology it is possible that the external speech processor and implanted stimulator unit may be combined to produce a totally implantable cochlear implant unit that is capable of operating, at least for a period of time, without the need for any external device. In such a device, a microphone would be implanted within the body of the user, for example in the ear canal or within the stimulator unit, and sounds would be detected and directly processed by a speech processor within the stimulator unit, with the subsequent stimulation signals delivered without the need for any transcutaneous transmission of signals. Such a device would, however, still have the capability to communicate with an external device when necessary, particularly for program upgrades and/or implant interrogation, and if the operating parameters of the device required alteration.
Much effort has gone into developing stimulation strategies to provide for device customisation in order to produce the best available percepts for the prosthesis recipient. Nevertheless it is acknowledged in the cochlear implant field that the percepts produced by pulsatile electrical stimulation often sound unnatural and somewhat harsh. Although many patients adapt to this sound and, after some time, even find it natural, this is not always the case and some patients may experience difficulties. In some instances in the past, for potential implant recipients having some amount of residual natural hearing, the expectation of harsh and/or unnatural sounding percepts produced by cochlear implants has been less attractive than simply persisting with unassisted residual hearing.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.